The company said the pack for Starbar was inspired by 1980s nostalgia and retro gaming machines.
Picnic has a redrawn logo typeface and a more modern feel.
Trade communications manager Susan Nash said: “We wanted to give them a refresh and make sure they were still relevant to consumers.
“Updating old favourites is always a challenge, but we’re really pleased with the results.
“Retailers should ensure they make the most of sales opportunities and stock the new look bars as they will be sure to grab consumers’ attention in-store.”